Electric discharge device



June 7, 1938. c. DEPEW ELECTRIC DISCHARGE DEVICE Filed April 8, 1952 2Sheets-Sheet l /N 5 N TOR c. DEPEW A 7'-TORNEV June 7, 1938.

c. DEPEW ELECTRIC DISCHARGE DEVICE Filed April 8, 1932 2 Sheets-Sheet 2FIG. 7

' INVEI VTOA C. DE PE W er I flmemam A TTORNEV Patented June 7, 1938UNITED STATES PATENT OFFICE Telephone Laboratories,

Incorporated; New

York, N. Y., a corporation of New York Application April 8,

8 Claims.

This invention relates to electric discharge devices and moreparticularly to such devices in whichgthe discharge is aided by agaseous atmosphere.

In three-electrode discharge devices in which an ionizing gas isemployed and the grid only controls the discharge under certainconditions of impressed voltage and gas pressure, it is expedient todetermine the operating characteris tics of the grid and moreovermaintain a uniform linear operating characteristic which will not beaffected by factors tending to vary the characteristic of the grid noraffect the discharge to such an extent as to alter the range over whichthe grid maintains control of the discharge.

In devices in which the grid functions as a trigger electrode, theoperating characteristic of the grid is controlled by the degree ofelectrostatic shielding which the grid presents to the passage ofelectrons between the cathode and the anode. Usually the grid surroundsthe cathode and ofiers a substantial electrostatic shield between thecathode and anode. However, the fact that the open ends of the gridoffer ionization paths between the cathode and anode causes thecharacteristic of the grid to extend over a wide range of thegrid-voltage, plate-voltage curve. Consequently, the control range ofthe grid is prolonged and may vary over wide limits before breakdown.

An object of the invention is to improve the operating characteristicsof a three-electrode discharge device in which gas is present as anionizing medium.

In accordance with one embodiment of this in-' vention, the electrodesof the discharge device are supported coaxially from a single stem inthe vessel and consist of a cylindrical cathode surface heated toemission temperature by a separate heating element, a cylindrical gridsurrounding and electrostatically shielding the complete length of thecathode, and an anode outside of the cathode and grid. An insulatingmember or barrier supported from the anode engages the supports of thegrid and cathode and serves as a shield forone end of the grid. Asimilar insulator supported independently of the anode" and extendingfrom the stem of the vessel closes the opposite end of the grid andserves as a spacer for the cathode and grid' coaxially extendingtherethrough. The device is filled with argonto a suitable pressure sothat the device operates as a trigger valve or relay.

It is evident that the insulating barriers at the ends of the grid andthe electrostatic effect of the grid which surroundsthe'cathode and ex-1932, Serial No. 603,996

tends substantially to the surface of the insulating barriers completelyshield the cathode. This shielding together with the length ofv the gridcauses the controlcharacteristics of the grid to simulate asubstantially straight line throughout the operating range of thedevice. Therefore, the control before breakdown may be regulated withinclose limits of grid potential.

A feature of the invention relates to the overall length of the.cathodeand grid with respect to the area of the anode. The elongated cathodestructure extends substantially the full length of the space between thepress and the top of the vessel and is surrounded by, a cylindrical gridof similar length, while the anode surrounds the cathode and grid onlyalong the intermediate portions thereof. This arrangement insures amaximum concentration of current density in the space discharge betweenthe cathode and anode. The various features of the invention will bemore clearly understood from the following detailed description inconnection with the accompanying drawings, in which:

Fig. 1 is a perspective view of one embodiment of the discharge devicemade in accordance with this invention with a portion of the enclosingvessel broken away to show the internal electrode assembly;

Fig. 2 illustrates a front elevation of the electrode assembly as shownin Fig. l with the enclosing vessel removed;

Fig. 3 is a side view in elevation of the electrode assembly shown inFig. 2;

Fig. 4 illustrates in perspective an enlarged segment of the insulatingdisc disclosed in the assembly of Fig. 1 to show the connection of thesupporting eyelet with the disc.

Fig. 5 is an enlarged view partly in section of the cathode and gridassembly illustrating the detailed structure of the cathode;

Fig. 6 shows another embodiment of the invention'in perspective in whichthe grid is substantially a solid wall member and the anode is oifsetwith respect to the axis of the cathode and grid;

Fig. 7 is an enlarged detailed view of the getter receptacle and themeans for supporting the getter pellet; and

Fig. 8 is a cross-sectional view of the stem shownin Fig. 6 along theline 8-8 of Fig. 6.

Referring to'the drawings, Fig. 1 illustrates one application 'of thefeatures of this invention in a discharge device comprising threeelectrodes enclosed in a glass vesselill, which is highly evacuated' andfilled with argon at a pressure of approximately two-tenths of amillimeter of mercury. The vessel is attached to a base supporting pinsor terminal prongs |2 which are connected to the electrodes within thedevice. The glass vessel ID is provided with an inwardly projecting stem|3 terminating in a flat press M in which are sealed the leading-inwires for the electrodes. Surrounding the stem I3 is a metallic collarl5 formed of two semi-cylindrical sections clamped together around thestem. Extending from the collar l5 are rigid rods l6 arranged in pairson opposite sides of the press l4. Each pair of rods is bent inwardlyabove the collar l5 and extends parallelly beyond the bent portion toengage the outer surfaces of a cylindrical metallic anode ll. This anodeis formed of two semi-cylindrical sections having outwardly extendedflanges l8 which are engaged by the upright rods l6 to support the anodefrom the collar I 5. One end of the flanges l8 of the anode is formedinto sockets |9 in which upright rods 20 are rigidly fastened bypressing in the sides of the sockets L9 or welding the rods 20 in thesockets. The rods 20 support a circular disc or barrier 2| of insulatingmaterial, such as mica.

The connection between the insulating material 2| and the rods 26 may beclearly understood from Fig. 4 which shows a portion of the discprovided with a tubular eyelet 22 which pierces the disc 26 and thetubular portion of the eyelet being slotted to provide four segments,two of the opposed segments being turned outwardly as shown at 23 andengaging the under surface of the disc 2| to rigidly attach the eyeletto the disc. The remaining segments of the eyelet embrace the rods 26and are welded thereto to rigidly fasten the disc to the upright rods.The mica disc 2| is made of large area to extend over the cylindricalboundary of the electrode assembly and being close to the wall of thevessel counteracts the electrostatic grid efiect of the glass wall. Thedisc 2| also serves as a centering means for the cathode structure shownmore clearly in Fig. 5 which consists of a central upright rod 24extending through a central aperture of disc 2| and welded to a bentextension 25 which is attached to one of the leading-in wires in thepress M. The weld between the upright rod 24 and the extension 25 formsa stop for a perforated insulating disc 26 which in turn forms a seatfor a tubular insulator 21 which surrounds the rod 24. A heater wire 28,preferably of tungsten, helically surrounds the insulator 21 and isthreaded through an insulator 29, seated on the tubular insulator andattached to the rod 24 as shown at 36. The opposite end of the heaterwire extends through the insulator 26 and is connected to a leading-inwire in the press M. The insulator 29 positioned on the end of thetubular insulator 21 together with the insulator 26 form spacing meansfor a cylindrical metallic cathode surface 3|, to prevent contact withthe heater element 28. The cathode surface 3| is attached to a supportwire 32 which is welded to one of the leading-in wires in the press I4and the cathode surface is coated with thermionically active material33, such as barium and strontium oxides. The large cathode surfaceinsures a copious supply of electrons which are emitted from thethermionically active material 33 and this supply of electrons isattracted to the anode I! which is considerably shorter than the cathodesurface to insure a concentrated current density in the space betweenthe cathode and anode.

Since the electrodes function in an atmosphere of gas, which may beargon or other inert gas or vapor, such as mercury, at a relatively lowpressure, for instance two-tenths of a millimeter of mercury, it isessential in order to control the discharge between the cathode andanode to insert a grid therebetween. Due to the configuration of thecathode and anode, the grid is in the form of a cylindrical helix. Thegrid consists of a cylindrical wire helix 36 having its laterals weldedto supporting upright parallel rods 34 and 35. The upright rods 34 and35 extend through apertures in the disc 2| and at the opposite endextend through a smaller diameter disc 31 which is situated within theboundary of the anode supports Hi. This disc also serves as a shieldbetween the cathode and the press I4. The disc 31 is provided withapertures near the periphery thereof in order to fit over support wires39 and 40 extending from the press l4 and the disc is supported fromthese wires by clips 38 which are provided with a bent portion to clampthe periphery of the disc '31 and a downwardly extended fluted portionwhich makes contact with the upright wires 39 and 40 in the press l4 andis welded thereto. The disc 3'! also maintains coaxial relationshipbetween the cathode structure and the grid since the support rods ofthese electrodes extend through the disc and accurately center thecathode structure within the grid structure. An extension on the uprightrod 34 is welded to the wire 39 which serves as a leading-in wire forthe grid 36.

In gaseous discharge devices employing a grid, the grid control ratio,that is, the ratio of anode voltage to negative grid voltage that willjust allow current to flow between the cathode and anode, is determinedon the one hand by the effectiveness of the grid as an electrostaticshield to control emission from the cathode to the anode and on theother hand by the amplification factor, which in gaseous devices, iscontrolled by the largest opening in the grid, in contradistinction tothe average effective opening in the grid in pure electron devices.Therefore, in order for the grid to effectively form an electrostaticshield around the cathode, it must extend beyond the whole length of thecathode in order to counteract end effects between the cathode andanode. If this fact were neglected, the open ends of the grid mayinadvertently determine the amplification factor of the device asrepresenting the largest effective opening of the grid. By making thegrid long, it shields the whole cathode and controls emission from thecathode to the anode. By the same reasoning, it is apparent thatshielding the ends of the grid by the insulating discs or barriers 2|and 31, it is possible to completely and electrostatically shield thecathode so that the discharge can only pass between the cathode andanode through the lateral openings. in the grid helix. Another advantageof the end shields of mica is the elimination of the unknown variablegrid effect of the glass wall of the vessel which may be introduced dueto the electrostatic field of the glass reaching the cathode and tendingto vary the grid control ratio. Finally the end shields tend tostraighten out the control characteristic of the grid so that the gridcontrol ratio is a constant throughout the operating range of thedevice. These advantages insure consistent and accurate grid control ofthe discharge between the cathode and anode whereby current flows to theanode instantaneously when the grid reaches the critical operatingcondition and further control of the current is transferred to theanode. The discharge may be disrupted by removing the potential appliedto the anode or by lowering the potential below a value necessary tosustain ionization. The voltage source for the anode i1 is supplied.through one of the prongs I2 on the base which is connected to aleading-in wire extending through the side of the stem l3. This wire isconnected to a strap 4| having its center portion welded to the collarl5 whereby a suitable potential may be applied to the anode H. The otherend of the strap 4| supports a rigid wire connected to a metallicgrooved ring 42 having pinched portions which hold strips of easilyvaporizable material, such as magnesium. This material is vaporized inthe final step of the exhausting process to absorb and fix residualgases within the vessel.

Another embodiment of the invention is shown in Fig. 6 which illustratesa gaseous discharge device in which grid control may be attained as inthe device described in Fig. 1; since in this figure the grid which isin the form of a metallic cylinder with a single opening for the passageof the discharge between the cathode and anode and in which the ends ofthe grid are closed, to completely control the emission from thecathode. In this device the enclosing vessel H1 is attached to a basesupporting contact prongs l2, the same as in the device of Fig. 1 andthe vessel is provided with an inwardly projecting stem |3 having apress M in which the leading-in wires for the electrodes are sealed. Apair of straight, vertical rods 43 and 44 extend from the press l4 andsupport a cylindrical metallic grid 45 in the form of twosemi-cylindrical sections fastened together and embracing the greaterportion of the rods 43 and 44. The grid is provided with a singleopening 46 which determines the amplification factor of the device. Thegrid 45 surrounds an indirectly heated cathode which is positionedcoaxially with respect to the grid 45 and is in the form of theconventional heater type cathode consisting of a quartz insulator 41enclosing a hairpin heater element having the ends connected to twospaced wires in the press I4. A metallic cathode surface 48 is wrappedaround the quartz insulator 41 and is coated with thermionically activematerials over an area within the boundary of the grid 45.

The ends of the grid 45 are closed by mica discs 49 and 50,respectively. These discs serve to center the cathode structure in theaxis of the grid 45, to completely shield the cathode so that emissionfrom the cathode takes place only through the opening 46 in the grid,and to eliminate the variable grid effect of the electrostatic field ofthe glass vessel Hi. The discs 49 and 56 are rigidly fastened to uprightwires 5i and 52 which are arranged longitudinally on opposite sides ofthe grid 45 in positions 90 from the rods 43 and 44, respectively.Theattaching means between the rods and the discs is the slotted tubulareyelet 22, described in connection with Fig. 4, and these eyelets areattached to the discs and. rods in the same manner as describedheretofore. The rods 5| and 52 are rigidly attached to outwardly bentwires 53 and 55 projecting from the press l4. The cathode 48 isconnected to the upright rod 5| by a cross-wire 55 so that a suitableconnection may be made to the cathode through one of the prongs l2, bentwire 53, upright rod 5| and cross-wire 55. In the same manner the bentwire 54 offers a means of supplying a suitable potential to the uprightrod 52 which, in the device shown in Fig. 6 serves as an anode and isplaced directly opposite the opening 46 in the cylindrical grid 45.

The upright rod 5| extends below the plane of the press l4 and carriesan inverted metallic cup 56, shown more clearly in Fig. 7. This cupcarries a pellet 51, of a thermit reaction mixture, such as magnesiumand aluminum. The pellet is held within the cup 56 by a resilientmetallic strip or clip 58 which positions the pellet in the flat portionof the cup and engages the inwardly turned edge of the cup 56. Thethermit reaction mixture is vaporized during the final evacuation periodof the vessel, to absorb residual gases in order that the inert gaseousfilling, such as argon, in the vessel will remain pure. The purpose ofusing a thermit reaction mixture as a getter material in the device asshown in Fig. 6 is to simplify the evacuation process since theelectrodes can be outgassed and the reaction mixture vaporized in asingle operation by surrounding the vessel with a high frequency coiland heating the electrodes by induction to free them of gas. Thevaporizing temperature of the reaction mixture is so high during theinitial heating of the electrodes that it does not vaporize. However,after a minute or two of heating the electrodes, all the gas is removedtherefrom and at the end of this interval the temperature is sufficientto vaporize the getter or reaction mixture to absorb the residual gases.This procedure simplifies to a great extent the manufacturing process ofthe device and materially reduces the cost of manufacture.

What is claimed is:

1. An electric discharge device comprising an enclosing vessel, acathode extending along the axis of said vessel, a grid having aplurality of turns surrounding said cathode throughout its length, ananode outside said grid, said cathode, grid and anode being immersed inan atmosphere of an inert gas at low pressure, and insulating shields incontact with the opposite end turns of said grid, one of said shieldsbeing substantially parallel to and close to an end wall of said vesseland the area of said shield being so proportioned as to counteract theelectrostatic grid effect of said vessel wall on said cathode.

2. An electric discharge device comprising an enclosing vessel having astem and an inert gaseous filling at low pressure, an elongatedcylindrical cathode surface supported above said stem, means for heatingsaid cathode to emission temperature, a cylindrical wire gridsurrounding said cathode throughout its length, insulating discsextending in planes coincident with the ends of said grid and centeringsaid cathode coaxially within said grid, and a cylindrical anodesurrounding said grid and cathode, said anode being proportioned andlocated intermediate the ends of said cathode and grid whereby maximumcurrent density concentration of the discharge is accomplished.

3. An electric discharge device comprising an enclosing vessel having astem, an inert gas in said vessel, a plate electrode supported from saidstem, an insulating member carried by said plate electrode at one endthereof, a cathode within said plate electrode and centrally supportedby said insulating member, a second insulating member supported fromsaid stem independent of said plate electrode, and a helical gridinterposed between said cathode and plate electrode, said grid havingits end turns in contact with said insulating members.

4. An electric discharge device comprising a vessel having a stem, aninert gas in said ves- I sel, an elongated cylindrical cathode, acentral support therefor, a cylindrical anode surrounding said cathode,an insulating member supported from said anode engaging said cathodesupport, an individually supported insulating member extending from saidstem and engaging said cathode support, and a helical electrodeshielding said cathode throughout its length, the ends of said electrodeengaging said insulating members.

5. An electric discharge device comprising an enclosing vessel having astem, an inert gas in said vessel, a collar surrounding said stem,upright supports extending from said collar, a flanged anode attached tosaid supports, wires extending from said anode, an insulating discattached to said Wires and extending across one end of said anode, asecond disc supported from said stem, the periphery of said disc beingWithin the boundary of said upright supports, a cylindrical cathode anda coaxial grid within said anode, said grid extending wholly within thelimits of said insulating discs, and supports for said cathode and gridprojecting through said discs.

6. An electric discharge device comprising an enclosing vessel having astem, an inert gas in said vessel, a collar surrounding said stem,upright supports extending from said collar, a flanged anode attached tosaid supports, wires extending from said anode, an insulating discattached to said wires and extending across one end of said anode, asecond insulating disc between said anode and stem, upright wiresextending from said stem and piercing said second insulating disc, acylindrical cathode supported between said discs along the axis of saidanode, a grid surrounding said cathode within said anode and extendingwholly within the limits of said insulating discs, and metallic clipsattached to said upright wires, said clips havin bent portions clampingthe peripheral edge of said second disc.

'7. An electric discharge device comprising an enclosing vessel havingan ionizable medium therein, a cathode, a cylindrical control electrodeencompassing said cathode, insulating discs electrostatically sealingthe ends of said control electrode, and an anode encompassing arestricted portion only of said control electrode.

8. An electric discharge device comprising an enclosing vessel having afilling of gas at a low pressure, a cathode, an enclosure for saidcathode comprising a helical grid encompassing said cathode andinsulating discs in immediate proximity to and extending across the endsof said grid, and a cylindrical anode of materially less length thansaid grid encompassing an intermediate portion of said grid.

CHARLES DEPEW.

